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xen-devel
[Xen-devel] Re: [RFC PATCH 02/33] Add sync bitops
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To: |
Arjan van de Ven <arjan@xxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [RFC PATCH 02/33] Add sync bitops |
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From: |
Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> |
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Date: |
Tue, 18 Jul 2006 11:18:45 +0100 |
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Cc: |
Andrew Morton <akpm@xxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Chris Wright <chrisw@xxxxxxxxxxxx>, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, Christoph Lameter <clameter@xxxxxxx> |
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Tue, 18 Jul 2006 03:19:16 -0700 |
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On 18 Jul 2006, at 10:56, Arjan van de Ven wrote:
plain text document attachment (synch-ops)
Add "always lock'd" implementations of set_bit, clear_bit and
change_bit and the corresponding test_and_ functions. Also add
"always lock'd" implementation of cmpxchg. These give guaranteed
strong synchronisation and are required for non-SMP kernels running on
an SMP hypervisor.
Hi,
this sounds really like the wrong approach; you know you're compiling
for xen, so why not just make set_bit() and the others use the lock'd
instructions at compile time?
Then all users of bitops would unnecessarily pay the price when running
in a single-CPU guest. Only a few of our bitops callers absolutely
require the lock prefix in all cases.
-- Keir
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